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More could take metformin

Up to 13% of patients with type 2 diabetes who could benefit from metformin currently face an absolute contraindication because of exaggerated concern about side-effects, a study suggests.

The researchers propose that only the 4% of diabetes patients with chronic kidney disease stage 4 should have an absolute contraindication to metformin. More than 17% are currently denied treatment because of fears about lactic acidosis in those with renal impairment.

The UK researchers said eGFR thresholds more accurately identified patients with significant kidney disease who could safely be prescribed metformin than traditional creatinine clearance measurements.

Their study concluded: 'The relationship between metformin treatment and lactic acidosis is, at best, circumstantial, and the benefits associated with metformin treatment are so great that current exclusions to treatment prohibit its use in too many patients.'

Under the proposals, published online in Diabetic Medicine, stage 4 CKD or greater would be an absolute contraindication to metformin, and CKD stage 3 would alert clinicians to consider other risk factors.

The researchers drew up the suggestions after calculating eGFR measurements from current metformin creatinine limits, and comparing the different measures of renal function in 12,482 type 2 diabetes patients.

They found that although many patients were currently barred from receiving metformin (21.8% of men and 13.5% of women), far fewer had CKD stage 4 (3.3% of men and 4.7% of women). Instead, 20.8% of men and 28.1% of women had CKD stage 3.

Men in particular were much more likely to be denied metformin using creatinine cut-offs, rather than eGFR thresholds.

Study leader Professor Eric Kilpatrick, consultant chemical pathologist at Hull Royal Infirmary, said: 'This is not because their renal function is necessarily poorer, but because they have a greater muscle mass which leads to higher creatinine concentrations in the blood. Moving to eGFR limits should help correct this imbalance.'